Brookite

Chemical Formula : TiO₂
Hardness : 5.5-6
Cleavage : Two, indistinct
Luster : Metallic adamantine
Color : Brown yellowish to reddish brown
Streak : White to grayish
Density : 4.14
Diagnostic Features and Trivia :
Crystal System and Habit : Orthorhombic; uncommon crystals are tabular {010}
Twinning : None
Polymorphs : Anatase and Rutile
Index of Refraction : alpha=2.583; beta=2.584; gamma=2.7